Estimating the O recombination probability in Pyrex from the loss frequency in oxygen-containing plasma

Surfaces interact with either active discharges or their afterglow in most plasma processes, via heterogeneous surface kinetics, that can affect both plasma and surface properties. In oxygen-containing discharges, the adsorption and recombination of atomic oxygen on reactor surfaces determine the gas composition and the availability of O for important volume reactions (e.g.: CO₂ + O → CO + O₂; CO + O + M → CO₂ + M). The effective rate of surface recombination is determined by a condition-dependent probability γ, that can be estimated from loss frequency measurements, and is often used as fundamental input parameter in models. The loss frequencies of O atoms have been measured in the positive column of O₂ and CO₂ glow discharges in a Pyrex tube (borosilicate glass), for several pressures, currents and wall temperatures [1]. However, the procedure for deducing γ from the loss frequency is not straightforward, since the processes determining the net losses of O are not known a priori. In this work, the Lisbon Kinetics (LoKI-B+C) simulation tool [2] is employed in steady-state and current-modulated modes to assess the processes determining the loss frequency and the most accurate way to estimate γ. The procedure developed allows not only to derive optimal values of γ, but also to assess the validity of different hypotheses on the most relevant processes for the net losses of O.

[1] Morillo-Candás et al., Plasma Sources Sci. Technol. 28 (2019) 075010

[2] Dias et al., Plasma Sources Sci. Technol. 32 (2023) 084003